Abstract
On-surface reactions based on Ullmann coupling are known to proceed on coinage-metal substrates (e.g. Au, Ag, Cu), with the chemistry of the surface strongly influencing the reaction progression. In addition, the topography of the surface may be expected to affect the local adsorption geometry of the reactants as well as the intermediate and final structures. Here, we investigate the effect of two different surface facets of silver, Ag(111) and Ag(110) on the formation of organometallic and covalent structures for Ullmann-type coupling reactions. Deposition of 4,4”-diiodo-m-terphenyl molecules onto either Ag(111) or Ag(110) surfaces leads to the scission of C-I bonds followed by the formation of organometallic zigzag structures, consisting of molecules connected by coordination bonds to Ag adatoms. The covalently coupled product is formed by annealing each surface, leading to the removal of Ag atoms and the formation of covalently bonded zigzag poly(m-phenylene) structures. Comparisons of the adsorption model of molecules on each surface before and after annealing reveal that on Ag(111), structures rearrange by rotation and elongation of bonds in order to become commensurate with the surface, whereas for the Ag(110) surface, the similarity in adsorption geometry of the intermediate and final states means that no rotation is required.
Highlights
On-surface reactions based on Ullmann coupling are known to proceed on coinage-metal substrates (e.g. Au, Ag, Cu), with the chemistry of the surface strongly influencing the reaction progression
Comparisons of the adsorption model of molecules on each surface before and after annealing reveal that on Ag(111), structures rearrange by rotation and elongation of bonds in order to become commensurate with the surface, whereas for the Ag(110) surface, the similarity in adsorption geometry of the intermediate and final states means that no rotation is required
There has been great progress in the development of on-surface synthesis of 1D and 2D covalently bonded structures. These have been created through a variety of different strategies[1,2,3,4,5,6,7] facilitating the synthesis of molecular chains,[8,9,10,11,12,13,14,15,16] graphene nanoribbons[17,18], and 2D molecular frameworks[19,20,21,22,23,24]. Such systems are readily studied by scanning probe microscopies, such as scanning tunnelling microscopy (STM) and atomic force microscopy (AFM), providing real-space imaging with sub-molecular resolution
Summary
On-surface reactions based on Ullmann coupling are known to proceed on coinage-metal substrates (e.g. Au, Ag, Cu), with the chemistry of the surface strongly influencing the reaction progression. There has been great progress in the development of on-surface synthesis of 1D and 2D covalently bonded structures These have been created through a variety of different strategies[1,2,3,4,5,6,7] facilitating the synthesis of molecular chains,[8,9,10,11,12,13,14,15,16] graphene nanoribbons[17,18], and 2D molecular frameworks[19,20,21,22,23,24]. This reaction has the advantage of creating covalent bonds between constituent molecules, making structures formed in this way more thermally stable than those formed through hydrogen bonds or van der Waals interactions. The relationship between the alignment of the intermediate and final structures with the substrate is an additional influential factor to be explored and is investigated here
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